[/quote] Is that really sufficiently real-time to help in such a situation? [/quote]

When you see weather coming or before you leave the mooring at quick look can tell you a lot.
While the AIS has been out on my VHF, I use it all the time on the Chesapeake Bay.
I can watch a freighter coming from miles away.

The Marine Traffic information on freighters tells where they have been and where they are heading and warns you if you are in danger.

Just another tool to help keep your boat safe.

Having AIS built into you chart plotter is a win win!